diff --git a/library/include/mobilisis/calculate_price.h b/library/include/mobilisis/calculate_price.h
index 17f1b2f..0681c73 100644
--- a/library/include/mobilisis/calculate_price.h
+++ b/library/include/mobilisis/calculate_price.h
@@ -171,7 +171,7 @@ CalcState CALCULATE_LIBRARY_API compute_price_for_parking_ticket(       // depre
 
 CalcState CALCULATE_LIBRARY_API compute_price_for_parking_ticket(
                                             parking_tariff_t *tariff,
-                                            QDateTime const &start_parking_time,
+                                            QDateTime &start_parking_time,
                                             int netto_parking_time,
                                             QDateTime &end_parking_time,    // return value
                                             struct price_t *price);         // return value